Re: RAID5 created by 8 disks works with xfs

[Jack Wang <jack.wang.usish@gmail.com>]

2012/4/2 John Robinson <john.robinson@anonymous.org.uk>
>
> On 02/04/2012 04:15, Jack Wang wrote:
>>
>> 2012/4/1 John Robinson <john.robinson@anonymous.org.uk
>> <mailto:john.robinson@anonymous.org.uk>>
>
> [...]
>>
>>    Now that you've suggested that, it occurs to me that for an
>>    application like this, the OP might be better doing his multiple
>>    slow streams to a spool folder on SSD, and copying over to the big
>>    array of spinning rust when each stream completes. 200 streams of
>>    500MB is 100GB of data, so a pair of slightly larger SSDs in RAID1
>>    (or RAID10, to balance the reads coming off) would do nicely as a
>>    spool area.
>>
>>    This might also be a good application for bcache, FlashCache or
>>    whatever.
>>
>> Using bcache/flashcache is what I'm considering, does above
>> configuration option still needed?
>
>
> Using a pair of SSDs? I think if you're adding a cache to a redundant array, you ought to make the cache redundant too.
>
> Using RAID10 to balance reads coming off the redundant pair of SSDs? That would depend on how bcache or flashcache is written; if it's single-threaded or does large copies from cache to the backing, then yes, you may see better performance or at least more balanced usage of the two SSDs, and surely won't see worse performance.
>
> Cheers,
>
> John.


John,

Thanks for reply , I mean using SSD as cache device, and raid5
16*7200rpm disks, is this works for streaming workload above?

I know bcache is try to turn rand write to seqencial write, but most
ssd is not good at RAND write as I know.

Cheers,

Jack
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